1. Field of the Invention
The present invention generally relates to flexible tanks for transporting liquids, and more particularly to flexible transportation tanks of the type comprised of a fluid resistant fabric material which, when filled, may be transported by air carrier to a desired location, and when emptied may be rolled and/or folded into a compact size for return transport and refilling.
2. Description of Related Art
Flexible containers are used for the handling, storage and transportation of large volumes of liquids, such as water or fuel, to remote sites. These containers are commonly referred to as bladder or pillow tanks, and they are typically rectangular so that they can be efficiently loaded onto vehicles for transportation. Examples of some prior art flexible liquid containers are found in U.S. Pat. No. 4,573,508 to Knaus and U.S. Pat. No. 5,499,743 to Blumenkron. Flexible liquid containers, such as exemplified in Knaus and Blumenkron, are typically made of a flexible fiber reinforced elastomeric material and have inlets or nozzles for filling and draining purposes. A principal advantage to such flexible liquid containers is that they are relatively lightweight and compact when not filled with a liquid since they do not have a frame or rigid supports. However, while they provide an efficient means of transporting large volumes of liquid, these kinds of flexible tanks have an inherent tendency to allow the free flow of liquid within them which can lead to liquid surges as a result of the acceleration and deceleration of the liquid. It has long been recognized that free flowing liquids can be dangerous to the balance and control of aircraft or vehicles.
As a solution to the above summarized problem, U.S. Pat. No. 3,288,186 to Headrick discloses a surge attenuating baffle and pillow tank combination. The baffle comprises a plurality of flexible, elongated, tapered pockets having opposite open ends. The pockets are disposed with their respective elongate extents substantially parallel with the direction of the surge of liquid in an elongate pillow tank. A base strip is directly secured circumferentially to the interior surface of the pillow tank transversely to the length of the tank. A baffle strip is then secured by grommets and laces to the base strip along regularly spaced alternatively converging and diverging lines on the base strip so that the pockets in their fully extended state have substantially semicircular cross sections. The disadvantage of this design is that the pockets or convolutions that attenuate the liquid surges in the tank are usually in a collapsed state when the liquid is at rest in the tank. Therefore, at least some initial movement of the surging liquid is required before the baffles extend and become operative in attenuating the surge of the liquid in the tank. As a solution to this problem, Headrick devised an improvement to his system of baffles, as described in U.S. Pat. No. 4,427,045, the improvement being that the baffles are made of a material that is flexible to allow collapse of the tank upon withdrawal of the liquid therefrom, but that is substantially shape retaining so that the hollow, truncated and tapered convolutions to be present in the tank when the liquid in the tank is at rest.
While the Headrick baffle systems may operate to attenuate some fluid surges in a flexible fluid tanks, the baffles introduce significant complexity and cost to the manufacture of the flexible tanks in which they are employed, and they also significantly increase the weight and bulk of the flexible tank when empty and thereby affect its collapsibility. Furthermore, while the Headrick flexible tank and baffle system may operate to attenuate some fluid surges in a flexible fluid tank in the longitudinal direction to the tank, they do very little to attenuate fluid surges in lateral directions. Dampening later fluid surges may be important in certain aircraft applications in which the tank is likely to encounter lateral acceleration in addition to longitudinal acceleration, such as for example in helicopter applications where the aircraft creates side-to-side movement (lateral acceleration) for the tank contents and front to back movement (longitudinal acceleration).
Accordingly there is a need for a flexible tank for transporting liquids having internal structures by which the significant wave or liquid current forces may be dampened, yet which do not add significant weight or bulk to the tank to significantly hinder the collapsibility of the tank, and which do not significant increase the time, materials and costs of manufacture of the flexible tanks. In some aspects, there is a need for a flexible tank for liquids having internal structures by which the significant wave or liquid current forces may be dampened in both longitudinal and lateral directions. The devices of the present invention are provided to fulfill one or more of these needs as will be understood from the following description.